The invention is directed to a rotatable cutting tool having a hard carbide insert affixed to a socket in an elongate body, and more specifically, to such a rotatable cutting tool designed so as to provide for improved performance characteristics. These characteristics include increased wear cycle, more efficiency through continuous penetration throughout the wear cycle, increased protection of the steel braze joint beneath the carbide, continued penetration in tougher milling conditions, and better bit rotation.
In the past, rotatable cutting tools have been put to a number of uses including use as a road planing tool in a road planing machine. Typically, a road planing machine includes a rotatable drum having a plurality of blocks affixed thereto. Each block contains a central bore therein. Road planing tools typically comprise an elongate steel body with a hard cemented carbide tip brazed into a socket contained in the forward end of the steel body. The steel body includes a reduced diameter portion adjacent the rearward end thereof. A retainer is adjacent the reduced diameter portion of the steel body. The retainer functions to rotatably retain the rotatable cutting tool within the bore of the mounting block during operation.
In operation, the drum rotates so as to cause the rotatable cutting tools to impact the road surface. The tools impacting the surface cut and break up the road surface. The road surface fragments are disposed of in a suitable fashion.
During the operation of the drum, each rotatable cutting tool rotates about its central longitudinal axis. It is important that the tool continue to rotate because adequate rotation is important to good performance. Heretofore, a number of designs of rotatable cutting tools have been used or described in patents and/or printed publications. However, most of these designs do not provide specific structure on the hard insert to enhance rotation. For example, U.S. Pat. No. 4,216,832 to Stephenson et al. concerns a rotatable tool wherein FIG. 10 illustrates a conventional hard cemented carbide insert. This insert includes a tip section. A generally frusto-conically shaped section is axially rearward of the tip section. A generally cylindrical flange section is axially rearward of the frusto-conically shaped section. A valve seat section is contiguous with and is positioned axially rearwardly of the generally cylindrical flange section. This cemented carbide insert does not present structure that enhances tool rotation.
Soviet Author's Certificate No. 899,916 concerns a rotatable cutting tool with a hard insert. The insert has a forward tip section with a generally conical shape. A cylindrical section is axially rearward of and contiguous with the tip section. A flange section is axially rearward of and contiguous with the cylindrical section. A radius joins the flange and cylindrical sections. A projection is axially rearward of and contiguous with the flange section. This hard insert does not show any structure that enhances the rotation of the tool.
European Patent Application No. 0122893 to Larsson et al. shows several styles of rotatable cutting bits. FIG. 1 shows one style. FIG. 2 shows another style. FIGS. 3 and 4 show a third style in which the hard insert has a tip section of a generally conical shape. A mediate section joins the tip section to a rearward section. The hard insert attaches at the rearward section to the bit body.
Swedish Patent Publication No. 436,433 to Lundell et al. shows two styles of rotatable cutting bits. The style shown by FIGS. 2. and 3 has a hard insert containing a recess in the rear surface. The recess has a shape that is complementary to that of a projection at the forward end of the steel body.
U.S. Pat. No. 4,497,520 to Ojanen concerns a rotatable cutting bit. The Ojanen patent says that it depicts a hard insert with coaxially aligned and integral sections. This hard insert does not show any structure or present any configuration that directly enhances tool rotation.
U.S. Pat. No. 4,725,099 to Penkunas et al. concerns a rotatable cutting bit. This patent says that it depicts a rotatable cutting bit of improved geometry. This bit has a hard insert with a conically shaped tip section, a base section contiguous with a first intermediate section, and a second intermediate section contiguous with the tip and first intermediate sections. This patent does not present any hard insert with a configuration that enhances the rotation of the tool.
U.S. Pat. No. 4,729,603 to Elfgen discloses a hard carbide insert having a series of circumferentially spaced grooves to provide a land-groove arrangement. These grooves serve to carry away material and assist to some degree in the rotation of the tool. Kennametal, Inc. once manufactured a hard carbide insert which utilized grooves in the conical portion of the insert. This hard carbide insert is shown in Kennametal Drawing DEV-C-1736 dated Jan. 31, 1980. Like the insert Elfgen depicts, these grooves serve to carry away material and assist to some degree in the rotation of the tool.